Holistic Analysis for Deadline Scheduled Real-Time Distributed Systems

Projet REFLECSThe holistic theory is a very interesting approach formerly proposed by Tindell and Clark~\cite{Tin94b} for assessing the feasibility of fixed priority real-time systems. Its major merit is to make the analysis of distributed systems tractable, without being at the same time too pessimistic. In this paper we extend the holistic theory to the analysis of deadline scheduled real-time distributed systems. Owing to its predictability, the Timed Token MAC protocol is assumed to arbitrate network accesses among host processors. Furthermore, in order to achieve a large resource utilization, outgoing packets are assumed to be locally queued earliest deadline first. A procedure for the computation of worst-case message communication delays is also given. The theory described in the paper is validated by means of a case study application, in which worst-case response times of {\em end-to-end} computations are tightly bounded. The example has confirmed the effectiveness of a global deadline scheduling approach

Analysis of Deadline Scheduled Real-Time Systems

Projet REFLECSA uniform, flexible approach is proposed for analysing the feasibility of deadline scheduled real-time systems. In its most general formulation, the analysis assumes sporadically periodic tasks with arbitrary deadlines, release jitter, and shared resources. System overheads of a tick driven scheduler implementation, and scheduling of soft aperiodic tasks are also accounted for. A procedure for the computation of task worst-case response times is also described for the same model. While this problem has been largely studied in the context of fixed priority systems, we are not aware of other works that have proposed a solution to it when deadline scheduling is assumed. The worst-case response time evaluation is a fundamental tool for analysing {\em end-to-end} timing constraints in distributed systems~\cite{Ti94b}

Preemptive and Non-Preemptive Real-Time UniProcessor Scheduling

Projet REFLECSScheduling theory, as it applies to hard-real-time environment, has been widely studied in the last twenty years and it might be unclear to make it out within the plethora of results available. Our goal is first to collect in a single paper the results known for uniproces sor, non-idling, preemptive/non-preemptive, fixed/dynamic priority driven contexts, consid ering general task sets as a central figure for the description of possible processor loads. Second to establish new results when needed. In particular, optimality, feasibility conditions and worst-case response times are examined largely by utilizing the concepts of workload, processor demand and busy period. Some classic extensions such as jitter, resource sharing are also considered. Although this work is not oriented toward a formal comparison of these results, it appears that preemptive and non-preemptive scheduling are closely related and that the analysis of fixed versus dynamic scheduling might be unified according to the concept of higher priority busy period. In particular, we introduce the notion of deadline-d busy period for EDF sched ules, that we conjecture to be an interesting parallel of the level-i busy period, a concept already used in the analysis of fixed priority driven scheduling

A population-based cohort approach to assess excess mortality due to the spread of COVID-19 in Italy, January-May 2020

Aims: To assess the impact of the COVID-19 pandemic on all-cause mortality in Italy during the first wave of the epidemic, taking into consideration the geographical heterogeneity of the spread of COVID-19. Methods: This study is a retrospective, population-based cohort study using national statistics throughout Italy. Survival analysis was applied to data aggregated by day of death, age groups, sex, and Italian administrative units (107 provinces). We applied Cox models to estimate the relative hazards (RH) of excess mortality, comparing all-cause deaths in 2020 with the expected deaths from all causes in the same time period. The RH of excess deaths was estimated in areas with a high, moderate, and low spread of COVID-19. We reported the estimate also restricting the analysis to the period of March-April 2020 (first peak of the epidemic). Results: The study population consisted of 57,204,501 individuals living in Italy as of January 1, 2020. The number of excess deaths was 36,445, which accounts for 13.4% of excess mortalities from all causes during January-May 2020 (i.e., RH = 1.134; 95% confidence interval (CI): 1.129-1.140). In the macro-area with a relatively higher spread of COVID-19 (i.e., incidence rate, IR): 450-1,610 cases per 100,000 residents), the RH of excess deaths was 1.375 (95% CI: 1.364-1.386). In the area with a relatively moderate spread of COVID-19 (i.e., IR: 150-449 cases) it was 1.049 (95% CI: 1.038-1.060). In the area with a relatively lower spread of COVID-19 (i.e., IR: 30-149 cases), it was 0.967 (95% CI: 0.959-0.976). Between March and April (peak months of the first wave of the epidemic in Italy), we estimated an excess mortality from all causes of 43.5%. The RH of all-cause mortality for increments of 500 cases per 100,000 residents was 1.352 (95% CI: 1.346-1.359), corresponding to an increase of about 35%. Conclusions: Our analysis, making use of a population-based cohort model, estimated all-cause excess mortality in Italy taking account of both time period and of COVID-19 geographical spread. The study highlights the importance of a temporal/geographic framework in analyzing the risk of COVID-19-epidemy related mortality

Characteristics of COVID-19 cases in Italy from a sex/gender perspective

Introduction: Coronavirus disease 19 (COVID-19) is an infectious disease caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). To date, few data on clinical features and risk factors for disease severity and death by gender are available. Aim: The current study aims to describe from a sex/gender perspective the characteristics of the SARS-CoV-2 cases occurred in the Italian population from February 2020 until October 2021. Method and results: We used routinely collected data retrieved from the Italian National Surveillance System. The highest number of cases occurred among women between 40 and 59 years, followed by men in the same age groups. The proportion of deaths due to COVID-19 was higher in men (56.46%) compared to women (43.54%). Most of the observed deaths occurred in the elderly. Considering the age groups, the clinical outcomes differed between women and men in particular in cases over 80 years of age; with serious or critical conditions more frequent in men than in women. Conclusions: Our data clearly demonstrate a similar number of cases in women and men, but with more severe disease and outcome in men, thus confirming the importance to analyse the impact of sex and gender in new and emerging diseases

Effectiveness of regional restrictions in reducing SARS-CoV-2 transmission during the second wave of COVID-19, Italy

To counter the second COVID-19 wave, the Italian government has adopted a scheme of three sets of restrictions (coded as yellow, orange, and red) imposed on a regional basis. We estimate that milder restrictions in regions at lower risk (yellow) resulted in a transmissibility reduction of about 18%, leading to a reproduction number Rt of about 0.99. Stricter measures (orange and red) led to reductions of 34% and 45% and Rt values of about 0.89 and 0.77 respectively

Impact of tiered restrictions on human activities and the epidemiology of the second wave of COVID-19 in Italy

To counter the second COVID-19 wave in autumn 2020, the Italian government introduced a system of physical distancing measures organized in progressively restrictive tiers (coded as yellow, orange, and red) imposed on a regional basis according to real-time epidemiological risk assessments. We leverage the data from the Italian COVID-19 integrated surveillance system and publicly available mobility data to evaluate the impact of the three-tiered regional restriction system on human activities, SARS-CoV-2 transmissibility and hospitalization burden in Italy. The individuals' attendance to locations outside the residential settings was progressively reduced with tiers, but less than during the national lockdown against the first COVID-19 wave in the spring. The reproduction number R(t) decreased below the epidemic threshold in 85 out of 107 provinces after the introduction of the tier system, reaching average values of about 0.95-1.02 in the yellow tier, 0.80-0.93 in the orange tier and 0.74-0.83 in the red tier. We estimate that the reduced transmissibility resulted in averting about 36% of the hospitalizations between November 6 and November 25, 2020. These results are instrumental to inform public health efforts aimed at preventing future resurgence of cases

Projet Re ecs

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Scheduling Aperiodic Tasks in Dynamic Priority Systems

In this paper we present five new on-line algorithms for servicing soft aperiodic requests in real-time systems, where a set of hard periodic tasks is scheduled using the Earliest Deadline First (EDF) algorithm. All the proposed solutions can achieve full processor utilization and enhance aperiodic responsiveness, still guaranteeing the execution of the periodic tasks. Operation of the algorithms, performance, schedulability analysis, and implementation complexity are discussed and compared with classical alternative solutions, such as background and polling service. Extensive simulations show that algorithms with contained run-time overhead present nearly optimal responsiveness. A valuable contribution of this work is to provide the real-time system designer with a wide range of practical solutions which allow to balance efficiency against implementation complexity

Efficient Aperiodic Service under Earliest Deadline Scheduling

In this paper we present four new on-line algo-rithms for servicing soft aperiodic requests in real-time systems, where a set of hard periodic lash is scheduled using the Earliest Deadline First (EDF) algorithm. All the proposed solutions can achieve full processor ulilization and enhance aperiodic responsiveness, still guaranteeing the ezecution of the periodic tads. Op-eration of dhe algorithms, performance, schedulability analysis, and implemenlation compleaity are discussed and compared with classical alternative solutions, such as background and polling service. Ezlensive simula-tions show that algorithms with contained run-time overhead present nearly optimal responsiveness. A valuable contribdion of this work is to provide the real-dime system designer with a wide range of practi-cal solu2ions which allow to balance eficiency against implementation complezity